Early antibiotics tied to increased asthma risk

NEW YORK (Reuters Health) - Babies given antibiotics within the first 6 months of life may be at least 50 percent more likely to develop asthma or allergies by their sixth birthday, suggests new research.

The finding adds to an already growing list of potential early life exposures that have been linked to later asthma, a chronic lung disease that affects about one in four urban kids across the developed world.

Previous studies have hinted at the role of antibiotics. But experts feared the results were unreliable since the drugs are commonly used for early asthma symptoms, which can look a lot like -- and therefore be mistaken for -- a lower respiratory tract infection.

"We tried to disentangle this association for children that did not have early respiratory tract infections or an early diagnosis of asthma," lead researcher Dr. Kari Risnes of St. Olav University Hospital, in Norway, told Reuters Health.

In the new study, Risnes and her Yale University colleagues followed 1,400 U.S. newborns for their first 6 years of life.

A third had been exposed to antibiotics by 6 months, and 12 percent developed asthma by age 6, report the researchers in the American Journal of Epidemiology.

Looking closer at these two groups, the team found that the risks of developing asthma or allergy by age 6 were both more than 50 percent greater among children exposed to antibiotics than among their peers who had not been prescribed the drugs.

When the researchers excluded kids that had a lower respiratory tract infection before age 1, the increased risk rose to 66 percent. (Nearly 70 percent of children with a history of respiratory infections had, in fact, taken antibiotics.)

The researchers found that the increased risk was even stronger -- nearly 90 percent -- among children with no family history of asthma.

Risnes and her team relate their findings to the so-called "hygiene hypothesis," the idea that early exposure to diverse microbes trains and tunes a baby's immune system, making it less prone to attack benign substances later.

"A lot of microbes, especially in the gut, are actually beneficial for the immune system," she added. "If you have antibiotics when you are a baby, this might imbalance this development of a healthy immune system."

This theory has also been behind several other recently investigated links with asthma and allergy, from breastfeeding to moms' contact with animals (see Reuters Health stories of April 28, 2010 and December 10, 2010).

Dr. Frank Gilliland of the University of Southern California, in Los Angeles, who was not involved in the new study, agreed with this explanation. However, he expressed concern in an e-mail to Reuters Health that the study relies on the mother's recall of antibiotic use up to 6 years after the fact, which may not always be accurate.

Still, both Risnes and Gilliland cautioned that antibiotics early in life should be used only when absolutely necessary.

Risnes' advice to parents: "You should accept antibiotics for a baby only after having a thorough examination."

"If you know what kind of an infection it is, you can often get more directed therapy," she said. "In babies, respiratory tract infections are mostly viral, and don't even benefit from antibiotics."